The present invention relates to expanded foam cartons and in particular to an expanded foam carton for storing and shipping eggs.
Since expanded foam egg cartons first came into popular usage, there have been many efforts to improve the egg cartons to decrease the incidence of egg breakage and to improve the versatility of the egg carton while maintaining the outer dimensions of conventional foam egg cartons. The present invention achieves these objectives by providing a novel thermo molded polystyrene foam egg carton which is provided not only with a novel structural configuration but is molded in accordance with novel molding methods.
Specifically, the present invention provides a unitary egg carton structure having a cover and a tray interconnected by a hinge apparatus defined by a pair of hinges connected by a hingeband. The tray of the thermo molded polystyrene egg carton includes at least one longitudinal partition member extending between opposite end walls and essentially bisecting the tray along its longitudinal dimension. A plurality of transverse partition members extend between the front and rear walls of the carton and intersect the longitudinal partition member for defining a plurality of cells in the tray. The walls of the longitudinal partition member and the transverse partition members intersect to define a contoured inner portion of the circumferential side wall for each cell where each contoured inner side wall portion extends upwardly from the tray base. The side wall of each cell is completed by the inside portion of the front, rear or end walls of the tray depending on the location of the cell. Each intersection between a transverse wall of a transverse partition member and a longitudinal wall of a longitudinal partition member defines a curved transition region.
In accordance with the invention, at least one expansion groove is impressed in each inner side wall for increasing its pliancy. By providing such a pliant inner side wall, each cell is capable of accepting a medium size egg but also being expandable to accept an egg as large as a jumbo size egg. Hence, a single egg carton structure can be used for all sizes of eggs. Such versatility is not possible in existing egg cartons because the cells in which the eggs are placed are substantially incapable of expanding to accommodate larger eggs. Therefore, several cartons having different sized cells are required to allow packaging of all sizes of eggs from the medium size up to the jumbo size.
An additional advantage provided by the pliant inner side walls of each cell is the capability of inserting an egg either pointed end down or pointed end up. Because of the circumferential rigidity of the inner walls of the cells in prior art cartons, the cells were designed to accept an egg pointed end down. Consequently, additional care had to be taken to assure that the egg was properly placed in the cell. Such is not required in the present invention. This is particularly advantageous since the lifting of government regulations requiring that eggs be stored and shipped with the pointed end down.
Still another aspect of the invention is the inclusion of a bendable flap which extends from and is part of the partition between adjacent cells of the carton. Such bendable flaps not only protect the eggs in adjacent cells from coming in contact with one another during shipping and handling of the carton but also provide a thinner pad between cells so that each cell will be capable of accommodating the larger eggs.
Heretofore, such thin resiliently bendable flaps were not incorporated because of perceived limitations on the capabilities of thermo molding polystyrene material. However, in accordance with the invention, it has been found that a thin polystyrene flap can be thermo formed utilizing a sheet of polystyrene with a nonexpanded skin on one side. Specifically, the thin flap can be formed by providing a female mold member with a cavity therein and a corresponding male mold member with a protrusion having a size and shape which is adapted to be inserted into the cavity of the female mold member. The polystyrene sheet with the skin side facing the male mold member is then positioned between the juxtaposed male and female mold members and the protrusion is then inserted into the cavity to a depth selected so that the minimum gap between the protrusion and the cavity is about one-tenth the thickness of the polystyrene. Further, the height of the male mold member protrusion and the depth of the female mold member cavity are selected so that the skin will stretch but the foam layer of the polystyrene sheet will rupture along a hinge region of the polystyrene sheet during the molding process. The result is a flap hinged to the top of the partition whereby the flap is resiliently movable relative to the remainder of the partition. The hinge is essentially the skin portion of the polystyrene sheet without the expanded foam layer thereon. Of course, such a flap end skin hinge may be provided on selected ones of the transverse partitions at selected locations along the longitudinal partition.
Still another feature of the carton in accordance with the invention is the incorporation of a centrally positioned cover support post which is integrally molded to extend from the interior surface of the cover. Of course, the post may be located at any position and more than one post may be provided. However, in the preferred embodiment, the cover support post is centered substantially about the centroid of the base portion of the cover.
It will be understood that heretofore such posts having a sufficient height to provide the necessary support function could not be thermo molded without producing a post with very thin walls and hence only limited structural support capabilities. The inability to mold such a cover support post resulted from the fact that cavities used to mold and post were vented. This venting caused the material comprising the walls of the post to be stretched to a thinness which made them incapable of providing substantial structural support. However, in accordance with the invention, it has been found that the utilization of an unvented cavity to form the post prevents a substantialy degree of stretching in the walls of post. Rather, the stretching of the material to from the post occurs to a great extent in the region of the base of the cover surrounding the post. Thus, a post can be formed which has a substantial wall thicknesses capable of providing the necessary support.
Finally, in accordance with the invention, the carton is provided with at least one hinge post which is integrally molded to protrude from the inside surface of the rear wall of the cover. The hinge post has a base portion extending laterally adjacent to the rear wall of the cover and a foot portion defining a longitudinal extension of the end of the base portion beyond the top edge of the rear wall of the cover by a distance which is less than the width of the hingeband between the pair of hinges connecting the cover to the tray. Additionally, a pair of recessed regions are provided in the hingeband so that the hinge post will seat in the recessed region of the hingeband when the cover is closed over the tray. Thus, the hinge posts prevent lateral movement of the cover relative to the tray when the cover is in closure relationship to the tray with the hinge posts seated in the recessed regions. This is particularly true when the hinge posts and the cover support post are both incorporated since the cover support post also prevents lateral movement of the cover relative to the tray when it is seated against the top of one of the partitions. When the carton employs a pair of spaced hinges with a hingeband therebetween, the hinge posts also serve to stabilize the cover on the tray and add compression strength to the back side of the carton. The depth of the posts can be varied to vary the amount of the strength of the carton. Thus, movement of the cover relative to the tray is substantially limited to vertical movement which is necessary to open or close the cover. The hinge posts may be strengthened by providing a generally concavely curved major surface facing the front wall of the cover.